如果用户在此选项卡中处于非活动状态，如何使倒计时暂停，如果处于活动状态，如何继续？

let countdownTimer;

function startCountdown() {
  let remainingTime = 10; // 以秒为单位
  countdownTimer = setInterval(() => {
    if (remainingTime <= 0) {
      clearInterval(countdownTimer);
      console.log("倒计时结束！");
    } else {
      console.log("剩余时间：" + remainingTime + "秒");
      remainingTime--;
    }
  }, 1000);
}

// 在页面加载完成后启动倒计时
window.addEventListener("load", startCountdown);

// 当用户离开当前选项卡时暂停倒计时
document.addEventListener("visibilitychange", () => {
  if (document.visibilityState === "hidden") {
    clearInterval(countdownTimer);
    console.log("倒计时已暂停");
  }
});

// 当用户回到当前选项卡时继续倒计时
document.addEventListener("visibilitychange", () => {
  if (document.visibilityState === "visible") {
    startCountdown();
    console.log("倒计时已继续");
  }
});